1. Field of the Invention
The invention relates to an optical disk apparatus, and more particularly, to an optical disk apparatus which subjects a plurality of optical disks to recording and reproduction.
2. Related Art
There has recently been developed an optical disk apparatus which has a plurality of light sources for emitting laser lights of different wavelengths and subjects a plurality of types of optical disks to recording and reproduction through use of the plurality of laser lights. Examples of such an optical disk apparatus include an optical disk apparatus which subjects a CD and a DVD to recording and reproduction; an apparatus capable of reproducing data from a CD and a DVD; an apparatus which records and reproduces data on and from a CD and which reproduces data from a DVD; and an apparatus capable of recording and reproducing data from and on a CD and a DVD. An apparatus which records and reproduces data on and from a CD and reproduces data from a DVD is taken as an example. The apparatus has two light sources: that is, a light source for a CD (simply called a “CD light source”) and another light source for a DVD (simply called a “DVD light source”). Laser light of recording power for recording data on a CD-R or a CD-RW is emitted from the CD light source. Further, laser light of reproduction power is emitted from the DVD light source. Here, the laser light emitted from the CD light source has a wavelength of about 780 nm, and the laser light emitted from the DVD light source has a wavelength of about 650 nm.
In order to record data on the CD-R, the recording power of the laser light emanating from the CD light source must be controlled to a desired value. For instance, in the case of a CD-R, a recording film is exposed to laser light, and a portion of the recording film is fused and evaporated by the thermal energy of the laser light, thereby forming a pit. Consequently, a deficiency or excess of recording power results in formation of a geometry failure, thereby deteriorating recording quality. Therefore, monitoring of intensity of the laser light of recording power, and feedback control for controlling the intensity of the laser light to a desired value are required.
Feedback control is achieved by, for example, providing a photodetector in the vicinity of the CD light source, providing a mirror in an optical path of the laser light emanating from the CD light source, causing the mirror to reflect a portion of the laser light so as to guide the reflected laser light to the photodetector, and detecting the intensity of the thus-guided laser light. More specifically, an optical system (optical pickup) is formed from a laser diode (LD), a collimator lens for converting into collimated light laser light emanating from the LD, and a mirror for reflecting the light emanating from the collimator lens toward an objective lens. A mirror is disposed on an optical path between the LD and the collimator lens, to thereby reflect and guide to a photodetector a portion of the laser light emanating from the LD. The power of the laser light that has been converted into an electric signal by the photodetector is supplied to a controller and an LD driver, thereby adjusting the value of a drive current for the LD driver.
However, in the case of the configuration in which a portion of the light traveling along the optical path is reflected and guided toward the photodetector, the light enters the objective lens, so that the power of the laser light to be radiated onto the optical disk decreases. Further, an optical component (i.e., a mirror) which is not essentially required for recording and reproducing data must be disposed on an optical path, thereby entailing an increase in the number of components, an increase in the size of the optical pickup, and a cost hike.